Report from Special Advisor (contribution to) NI Assemble, Committee for the Environment, Report on the Committee’s Inquiry into Wind Energy

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Overview – keypointsAcoustic terms: LAeq,T is the ‘average’ of the total sound. LA90,T is the background sound when the loudest elements are ignored. LAeqT and L90 do not take account of the type of the sound. Sound reduces with increasing distance from the source and is affected by weather and the landscape. At a distance of 1km you mainly only hear the low pitch (frequency) sounds.Mechanical noise from wind turbines is generally the result of faults or wear and tear. Most wind turbine noise is not mechanical, it is aerodynamic noise ie ‘swish’. The sound from turbine blades is not steady, it fluctuates, this is called amplitude modulation (AM). Wind turbine noise can also contain noticeable tones. Generally, sounds containing tones more annoying. Wind turbine noise is more annoying than transport noise or noise from other industries. Reasons for recommendation that ETSU-R-97 is updatedModern wind turbines are considerably larger now than in those that were in place in 1997, this can result in more lower frequency noise and an increased risk of AM due to high level wind fluctuations. ETSU - R - 97 The Assessment and Rating of Noise from Wind Farms’ is influenced by BS4142 Method for rating industrial noise affecting mixed residential and industrial areas. BS4142 is currently being updated. The draft revised BS4142 includes further emphasis on the annoyance from tones and fluctuations. The draft proposes that when both characteristics are present the two should individually be taken into account.The WHO guidance for indoor noise levels at night was 35dB when ETSU-R-97 was published in 1997, it has now been revised to 30dBETSU-R-97 advises using the LA90,10min noise index for both turbine and background noise. Most other relevant standards use LAeq for source noise. LA90 was adopted by ETSU-R-97 as it was assumed at the time of drafting that wind turbine noise was relatively steady and characterless. Evidence and knowledge since 1997 has highlighted that certain wind farms/single wind turbines produce AM and hence the original assumption within ETSU-R-97 that wind turbine noise was relatively steady and characterless no longer holds true. ETSU-R-97 needs to be updated to take account of much greater understanding of the acoustics of large wind turbines and the annoyance/health effects of wind turbine noise. In particular, consideration of the following content of ETSU-R-97 is recommended: • The statement that it is not necessary to use a margin above background approach in low-noise environments• The use of LA90 for both the background noise and the wind farm noise • Night time limit of 43dBA bearing in mind the revised WHO guidelines• The assumption that background noise rises with increasing wind speed• The consideration of fluctuations and tones.Specific issuesMore recent designs of wind turbines are much quieter than older designs. Many industries are required to apply Best Available Techniques (BAT) to prevent noise disturbances. The enquiry may wish to consider the age and type of turbines being proposed for installation in Northern Ireland. Anecdotally, many “new” wind turbines installed in Northern Ireland (NI) are in fact reconditioned turbines. On-going, long term monitoring by the developer would enable the continuing noise exposure of the nearby residents to be determined and increases in noise, beyond the predicted and permitted levels, to be identified and remedied.It is common practice for local planning authorities to set planning conditions to control or reduce noise levels, or to mitigate the impact of noise. Examples relating to wind turbine noise are provided in the IOA Good practice guide to the application of ETSU-R-97.There is a great deal of expertise within the Environmental Health profession in Northern Ireland’s district councils. There is a considerable burden, on individual councils, associated with contributing to planning applications regarding wind turbines.It is suggested that a more strategic approach to both single turbine and wind farm applications would be beneficial, as opposed to the ad hoc approach currently employed in Northern Ireland. Danish policy The Danish policy includes• a replacement Scheme for Wind turbines on land • a recent emphasis on a planned and coordinated development of offshore wind farms • a loss of value scheme for dwellings• the option to purchase scheme. Erectors of large wind turbines shall offer for sale at least 20% of the wind turbine project to the local population.
Original languageEnglish
PublisherNI Assembly
Number of pages2
Publication statusPublished (in print/issue) - 29 Jan 2015


  • Wind turbine
  • noise
  • environment
  • acoustics


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